Difference between 'Level Instance' and'Packed Level Actor'

I have watched a couple of tutorials on creating ‘Level Instances’ and ‘Packed Level Actors’ , in one of the tutorials the author stated that…“there is no need to use different meshes, Nanite performs better if you use the same mesh”, but then seems to contradict himself by bringing in many different types of trees, bushes, tree stumps, branches etc to create his ‘Level Instance’. So is bringing in a whole variety of Foliage type assets acceptable when creating a ‘Level Instance’. And also can anyone tell me what is the benefit of a ‘Packed Level Actor’ again watched a a number of videos but am a little confused as in one video the author seems to just select a tree and right click and select ‘Create Packed Level Actor’ not really sure why. Any pointers or help will be most appreciated, Thank You